Lightning risk assessment software
What to compare when you choose software or a lightning risk assessment calculator for IEC 62305-2:2024, NFPA 780-2026 Annex L or AS 1768:2021: the edition behind the numbers, the standards it runs, whether you can see the working, and the report a reviewer signs.
Every lightning risk assessment tool implements a method one of three standards defines. What differs between tools is which standards and editions they compute, and what you can prove afterwards.
The three methods are IEC 62305-2:2024, used across most of the world; the informative Annex L of NFPA 780-2026, used in the United States; and Section 2 of AS 1768:2021, used in Australia. The tools that run them are few: some desktop packages, a few browser tools, calculation modules inside larger electrical suites, and a very large number of spreadsheets. Most compute their chosen method correctly. The differences that matter on a real project are narrower than a feature list suggests: the edition behind the numbers, whether a coefficient can be traced to the clause it came from, and whether the output is a report a reviewer will sign.
This page sets out what to compare, whatever tool you are looking at. It names no vendor: software releases change, so treat it as a checklist and confirm anything decisive with the vendor before you buy. Each standard must be bought from its publisher for design work.
What to look for in lightning risk assessment software
Seven questions decide most of the choice. Price and platform sit below them, not above.
Which edition it computes on
IEC 62305-2:2024, NFPA 780-2026 and AS 1768:2021 are the current editions. Each changed the method from the one before, so a result on an older edition is a different result. This is the question most worth asking, and the one marketing pages answer least clearly.
Which standards it runs
A tool may run one standard, or several. Where it runs more than one, check each runs as its own method with its own tables. NFPA 780 and AS 1768 resemble IEC's older model, but none of their values may be swapped for an IEC value.
A calculation trace
A reviewer who questions one coefficient needs more than a final number. Opening a figure to see the table or equation it came from is what turns a calculation into evidence. See traceable, not AI-generated.
National departures
Under IEC 62305-2:2024 national practice can change the arithmetic: Germany holds rp at 1, Greece holds PTWS at 1, and the Introduction lets national or local regulation fix the tolerable risk. NFPA 780 and AS 1768 have no such list. See IEC 62305 around the world.
What the reviewer actually reads
The deliverable is a document, not a screen: the standard and edition, inputs with sources, the method, results per IEC zone or per NFPA or AS type of loss, the verdict against each tolerable value, and the measures. See audit-ready risk reports.
Reviewer sign-off
An engineer signs the result, and on many projects a second person reviews it first. Look for a review step and a signature block in the tool itself, so the issued report is the reviewed one and not a later edit.
A record of who changed what
When a figure is questioned months later, the answer is in the history: who changed an input, when, and who approved it. A spreadsheet rarely keeps that record. Software should keep it without anyone having to remember to.
What to check for each standard
Ask a vendor these questions for each standard you work to. Read the values themselves from each standard.
| IEC 62305-2:2024 | NFPA 780-2026 Annex L | AS 1768:2021 | |
|---|---|---|---|
| The method it must run | One risk R for injury and physical damage, plus a frequency of damage F for internal systems (clauses 7.3, 9.1) | The simplified risk assessment of ND against NC (L.5), and the detailed method with up to four risks, R1 to R4 (L.6) | Four risks, R1 to R4 (Appendix B, B.2.2), with the selection process of Figure 2.1 |
| How the verdict is taken | Per risk zone (clause 7.3), never on a structure average | Per relevant type of loss (L.6.5), never on the printed total R = R1 + R2 + R3 + R4 | Per type of loss, then surge protection alone where RA plus RB is below RT (Figure 2.1 footnote a) |
| Tolerable values it should let you set | RT, 10⁻⁵ as a representative value (7.3 NOTE 1), and FT, 0,1 or 1 (9.3 NOTE 1) | Defaults for R1 to R3 in Table L.6.2, changeable under L.6.2. No R4 default, so someone has to supply one | Typical values for each type of loss (Table 2.1). Economic loss is the owner's choice (Table 2.1 NOTE); the tool sold with the standard applies a different value to cultural heritage than Table 2.1 prints |
| Density input | Ground strike-point density NSG (Annex A) | NSG, or 1.7 times a flash density (L.2.2) | Ground flash density Ng, Figure C.1 (C.3.1) |
| The trap to ask about | Whether national departures are applied before the calculation, and which jurisdictions it holds | The Figure L.6.8 worksheet still writes NG, and works NL from AI and CD, where the body text uses NSG, AL and CE (L.6.6.1.3). A tool copied from the worksheet carries those slips | The spreadsheet supplied with the standard holds the working that the printed text summarises (Clause 2.5.3), so ask which version of it the software reproduces and what it was checked against |
For the methods themselves, read NFPA 780 Annex L explained, AS 1768 explained and the IEC 62305-2 risk method. How the US and international methods differ is covered in NFPA 780 vs IEC 62305.
The kinds of tool you will find
Most tools fall into one of four kinds. Each suits a different team, and each deserves the same checklist above.
Desktop packages
Installed software licensed per workstation or per network. They work offline, which suits a single engineer and some IT policies. Each installation is updated on its own, so on a team two engineers can end up on different releases. Ask which edition the current release computes on.
Modules in an electrical suite
A risk calculation inside a wider electrical engineering package. A reasonable fit for a team already modelling the whole electrical system there, and an expensive route for a firm that only needs the assessment. Check which standards and editions the module quotes.
Free browser calculators
Quick and often free, some with a choice of standard or edition. Useful for a first check. Look at what the output contains before relying on one for a deliverable, because a number on screen is not a report an auditor will accept.
Browser workspaces
Software in the browser where a team shares projects, the calculation is updated centrally, and the output is a finished report. Check which standards each one runs, and, for IEC work, whether it can express the jurisdiction you work in.
What a lightning risk assessment calculator can and cannot do
A lightning risk assessment calculator takes the inputs of one method and returns its numbers. That is the core of the job, and a good one gets the arithmetic right. What a calculator usually does not do is everything around the arithmetic: keep the inputs with their sources, record who changed what, hold a review step, and produce a report someone can sign and file.
Some methods suit a calculator better than others. The NFPA 780-2026 simplified risk assessment in Section L.5 is short: the strike-point density NSG, a collection area, a location factor, four coefficients from Tables L.5.1.2(a) to (d) and the tolerable frequency NC of equation (L.5.1.1). The detailed NFPA method, the full IEC 62305-2:2024 method and the AS 1768:2021 method all take far more inputs, and that is where a missing trace starts to cost hours in review. A critical facility under NFPA 780-2026 L.5.3.2 should not rest on the simplified risk assessment alone anyway.
Spreadsheets, and why they persist
More lightning risk assessments are produced in spreadsheets than in any single piece of software. That is not a failure of judgement. The methods are arithmetic, a spreadsheet implements arithmetic, and a careful engineer who owns the file and knows the standard can produce a sound result in one. In Australia the spreadsheet is part of the standard: AS 1768:2021 Clause 2.5.3 provides one for standalone structures, first issued with AS/NZS 1768:2007, and applies the Appendix B method through it.
The problems are practical, and they arrive with time. A file built against a superseded edition does not notice that the standard has moved on. A copy taken for one project and edited becomes a second, quietly different, method. There is rarely a record of who changed a coefficient or why, which is exactly what a reviewer asks about. And the output has to be assembled into a report by hand every time, which is where the hours go.
The honest test is not whether spreadsheets can do the job. It is whether the specific spreadsheet in front of you is on the current edition, whether anyone can say who last changed a coefficient, and whether the version used on this project is the one that was reviewed. If all three answers are good, keep it. If any of them is a shrug, that is the reason to move.
How to check an edition claim yourself
Vendor pages are often vague about the edition, and not always deliberately. A page written three years ago says what was true three years ago. Two checks settle it quickly.
First, ask for the exact standard designation the software prints on its own report, with the year. A tool on the current editions prints IEC 62305-2:2024 (or an adoption such as EN IEC 62305-2:2024), NFPA 780-2026 or AS 1768:2021. A 2006, 2010 or 2012 IEC designation, NFPA 780-2020 or AS/NZS 1768:2007 means an older model. The report heading is more reliable than a marketing page, because it is what a reviewer sees.
Second, ask a method question the editions answer differently. For IEC: does the tool take ground strike-point density or flash density, does it produce a single risk R for injury and physical damage or four separate risks, and does it have a frequency of damage F for internal systems? A tool on the 2024 edition answers the first way to all three. For NFPA 780: does the Annex L density input use NSG, or a flash density multiplied by 1.7 under L.2.2? The 2020 edition used flash density, so a tool that asks only for NG with no conversion is on the older model. For AS 1768, see AS/NZS 1768:2007 vs AS 1768:2021, and for NFPA, what changed in NFPA 780-2026.
The tolerable risk is not a constant
Any tool that hardcodes the tolerable risk is asserting something none of the three standards does. IEC 62305-2:2024 clause 7.3 NOTE 1 gives RT = 1 × 10⁻⁵ per year as a representative value and allows another once the case has been investigated in detail, and its Introduction lets national or local regulation fix RT, the tolerable frequency of damage FT, and the Annex A, B, C and E rules and values. NFPA 780-2026 L.6.2 calls its Table L.6.2 values defaults and lets the owner, a representative or the AHJ choose others. AS 1768:2021 calls its Table 2.1 values typical, and leaves the economic loss value to the owner.
What we built, and what we have not
New to the methods? Start with lightning risk assessment explained, or try the free rolling sphere calculator with no signup. Designing the physical system rather than choosing a tool? See lightning protection system design.
Questions answered
What software is used for lightning risk assessment?
What should I look for in lightning risk assessment software?
How do I know which edition a tool uses?
Does the edition my software uses actually matter?
Is there a free lightning risk assessment calculator?
How much does lightning risk assessment software cost?
Can I do a lightning risk assessment in Excel?
Is desktop or cloud better for lightning risk assessment?
Can one tool run IEC 62305, NFPA 780 and AS 1768?
The tolerable risk in IEC 62305-2 is not a fixed constant.
Clause 7.3 NOTE 1 gives RT = 1 × 10⁻⁵ per year as a
representative value of tolerable risk and adds that another value may be set once
the case has been investigated in detail. The standard's introduction then lets national or local regulations fix
RT, the tolerable frequency of damage FT
Get started today